Re: [PATCH bpf 1/2] bpf: fix alignment of netns_dev/netns_ino fields in bpf_{map,prog}_info

On 05/29/2018 07:17 PM, Song Liu wrote:

On Sun, May 27, 2018 at 4:28 AM, Eugene Syromiatnikov [off-list ref] wrote:

quoted

Recent introduction of netns_dev/netns_ino to bpf_map_info/bpf_prog info
has broken compat, as offsets of these fields are different in 32-bit
and 64-bit ABIs.  One fix (other than implementing compat support in
syscall in order to handle this discrepancy) is to use __aligned_u64
instead of __u64 for these fields.

Reported-by: Dmitry V. Levin <redacted>
Fixes: 52775b33bb507 ("bpf: offload: report device information about
offloaded maps")
Fixes: 675fc275a3a2d ("bpf: offload: report device information for
offloaded programs")

Signed-off-by: Eugene Syromiatnikov <redacted>
---
 include/uapi/linux/bpf.h       | 8 ++++----
 tools/include/uapi/linux/bpf.h | 8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c5ec897..903010a 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -1017,8 +1017,8 @@ struct bpf_prog_info {
        __aligned_u64 map_ids;
        char name[BPF_OBJ_NAME_LEN];
        __u32 ifindex;
-       __u64 netns_dev;
-       __u64 netns_ino;
+       __aligned_u64 netns_dev;
+       __aligned_u64 netns_ino;
 } __attribute__((aligned(8)));

Shall we add a __u32 padding variable before netns_dev? We can use it
for in the future.

Agree with Song, and definitely prefer that approach since we already use the hole
as a bitfield in net-next; like this https://patchwork.ozlabs.org/patch/924415/.